Fluid handling – With heating or cooling of the system – With electric heating element
Reexamination Certificate
2000-07-10
2001-05-08
Chambers, A. Michael (Department: 3753)
Fluid handling
With heating or cooling of the system
With electric heating element
C137S625300, C137S629000, C251S319000, C118S620000
Reexamination Certificate
active
06227236
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a valve disposed in an exhausting line of an evacuation device such as a CVD (Chemical Vapor Deposition) device in order to stop/start exhausting gas flow and to control evacuation conductance automatically. More particularly the present invention relates to a widely variable conductance valve driven with an electric motor which is applicable to controlling of process gas in a semiconductor fabrication process using a reduction pressure CVD device, for example.
To describe an evacuation device where a valve of the present invention may be used, function of a valve will be described below referring to a major semiconductor fabrication device, for example.
FIG. 1
generally illustrates a device applicable to system of semiconductor fabrication such as a reduction pressure CVD device.
The reference sign A depicts an evacuation pump, B depicts a variable valve, and C does a reaction chamber where a work to be processed is placed. The reaction chamber C is connected with a process-gas supply E through a mass-flow controller D. The reference sign F depicts a vacuum gauge for monitoring pressure in the reaction chamber C. A pressure signal detected by the vacuum gauge F is transmitted to an automatic pressure controller G to be compared with a predetermined pressure signal so as to output a drive signal for adjusting an opening degree of the variable valve B. The drive signal adjusts the opening degree of the variable valve so that the pressure in the reaction chamber C is controlled to be the predetermined pressure. Further, the reference sign H is a heater for heating the reaction chamber C.
A silicon wafer I to be processed is placed in the reaction chamber C which is connected with the process gas supply E, and the valve B is opened to evacuate the reaction chamber C down to a target pressure, about 0.5 Pa. Then a process gas such as NH
3
(ammonia) is introduced into the reaction chamber C from the process-gas supply E via the mass flow controller D so as to regulate the opening degree of the variable valve B to be a predetermined pressure, about 133 Pa, monitoring the pressure in the reaction chamber C with the vacuum gauge F. Upon supply of the process gas and suction of the gas by the evacuation pump A via the valve B, the silicon wafer I is deposited under the predetermined pressure of the process gas. During the process the reaction chamber is controlled by the opening degree of the valve B to be at the predetermined pressure. Further, on completion of the process, the introduction of the process gas is stopped, and the valve B is fully opened to evacuate the reaction chamber C to the target pressure. The variable valve B is then fully closed to increase the pressure in the reaction chamber C up to the atmospheric pressure, thereby taking finished products out of the chamber.
FIG. 2
exemplifies a conventional variable valve used in the above device.
The reference numeral
101
depicts a throttle valve body having a flange portion
101
b
circumscribing a fluid passage
101
a
. The numeral
102
is a disc-shaped valve body having almost the same diameter as that of the fluid passage
101
a
of the throttle valve body
101
, and the valve body
102
is openably mounted at the fluid passage
101
a
. The reference numeral
103
depicts a drive shaft for connecting the valve body
102
with a valve drive portion
104
. The drive shaft
103
is connected with the valve body
102
by means of a pin
105
so as to turn integrally with the valve body
102
. A drive means within the drive portion
104
turns the drive shaft
103
to rotate the valve body
102
and change an opening area of the fluid passage
101
a.
As mentioned above, during the process the pressure in the reaction chamber C must be controlled within a wide range from the atmospheric pressure (1013 HPa) to a few Pa. Further, a pressure around the few Pa, the lowest limitation of the range, must be finely controlled. In the conventional variable valve which is a throttle valve, the valve body
102
may be turned to control the process gas to be a few Pa but cannot prevent leakage when fully closed because of its structure. On completion of the process, the pressure in the reaction chamber C is brought to the atmospheric pressure. Thus, even if the valve is fully closed, the valve is not able to be completely isolate the reaction chamber C from the evacuation pump A. Therefore an isolating means has been separately needed.
Most process gases used in semiconductor fabrication liquefy at an ambient temperature. When a process gas is cooled down, it may be deposited on an inner wall of a device. It may also be deposited on outer surfaces of the valve body or inner surfaces of a flange. As such deposition increases, an appropriate adjustment of an opening degree may not be completed. In the worst case, the valve body would not move to open or close. Then, such a throttle valve is disassembled to clean its valve body, inner surface of flange etc. However such disassembling and cleaning is troublesome. Further, most of process gases are toxic and dangerous, and care should be taken to handle these process gases. Such a conventional valve may have heaters on at a valve body and a flange portion to prevent deposits of materials, whereby simplifying such device and decreasing the number of components.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a widely variable conductance valve which control a flow rate of a process gas used in a semiconductor fabrication device by means of only one control valve and to adjust a pressure in a reaction chamber from the atmospheric pressure to a substantial vacuum pressure, thereby simplifying the structure of the device.
Another object of the present invention is to provide a widely variable conductance valve, comprising:
a tubular valve chamber;
an inlet for connecting with a reaction chamber;
an outlet for connecting with an evacuation pump;
a short tubular valve seat mounted at the outlet, the valve seat having a pipe joint formed downstream and a circumferential flange portion formed upstream;
a valve body disposed in the valve chamber, the valve body being movable back and forth against the valve seat;
a first disc-shaped valve body portion having a diameter to stop a fluid, the first valve body portion being in contact with the flange portion;
a second disc-shaped valve body portion screwed on an end surface of the first valve body portion, wherein the first and second valve body portions are aligned, the second valve body portion has almost the same diameter as an inner diameter of a valve hole of the valve seat so as to be inserted into the valve hole; and
a tapered notch formed at the second disc-shaped valve body portion, depths of the tapered notch being gradually decreased from downstream to upstream.
Another object of the present invention is to provide a widely variable conductance valve comprising a plurality of notches at a circumference of the second valve body portion.
Another object of the present invention is to provide a widely variable conductance valve in which cross sectional area and shape of each notch are determined according to a range of flow rates to be controlled and a moving distance of the second valve body portion against the valve seat.
Another object of the present invention is to provide a widely variable conductance valve comprising a plurality of second valve body portions having a plurality of notches of different numbers and of different shapes so as to exchange one of valve body portions with another according to a range of flow rate to be controlled and a flow characteristic.
Another object of the present invention is to provide a widely variable conductance valve in which the valve body is moved against the valve seat by a piston rod connected with a valve drive portion constructed of a gear box and an electric motor, the piston rod being inserted into the gear box via a partition mounted at opposing side to the outlet and a sealing mechanism.
Another object
Kusumoto Satoru
Oka Ryoichi
Chambers A. Michael
Jordan and Hamburg LLP
McShane Thomas L.
Megatorr Corporation
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